Differential Diagnosis for Tibialis Anterior Weakness Sparing the Tibialis Posterior
- Single Most Likely Diagnosis
- Peripheral neuropathy (specifically, peroneal neuropathy): This is the most likely diagnosis because the tibialis anterior muscle is primarily innervated by the deep peroneal nerve, a branch of the common peroneal nerve. Damage to this nerve can cause weakness in the tibialis anterior while sparing the tibialis posterior, which is innervated by the tibial nerve.
- Other Likely Diagnoses
- L5 radiculopathy: The L5 nerve root innervates the tibialis anterior muscle. Compression or damage to this nerve root can cause weakness in the muscle it supplies, potentially sparing the tibialis posterior, which is primarily innervated by the tibial nerve (S1 and S2 roots).
- Anterior compartment syndrome: Increased pressure within the anterior compartment of the leg can compress the nerves and blood vessels supplying the tibialis anterior, leading to its weakness. The tibialis posterior, located in the deep posterior compartment, might be spared.
- Do Not Miss Diagnoses
- Diabetic amyotrophy: Although less common, diabetic amyotrophy (also known as diabetic lumbosacral radiculoplexus neuropathy) can cause asymmetric muscle weakness, including the muscles of the lower extremities. It's crucial not to miss this diagnosis due to its association with diabetes management and potential for significant morbidity.
- Vasculitis (e.g., giant cell arteritis, polyarteritis nodosa): Vasculitis affecting the blood supply to the nerves or muscles could lead to focal weakness. While less likely, missing this diagnosis could have severe consequences due to the potential for widespread vascular involvement.
- Rare Diagnoses
- Inclusion body myositis: A rare inflammatory muscle disease that can cause progressive muscle weakness, potentially affecting the tibialis anterior more significantly than the tibialis posterior in some cases.
- Focal myopathy: A rare condition where there is localized disease of the muscle, which could theoretically affect the tibialis anterior and spare the tibialis posterior, though this would be an unusual presentation.
- Hereditary neuropathies (e.g., Charcot-Marie-Tooth disease): Certain types of hereditary neuropathies can cause asymmetric muscle weakness, including involvement of the lower extremities. However, the pattern of tibialis anterior weakness sparing the tibialis posterior would be atypical.